Speaker "hum" or interference

Hey, I have my desktop connected to my reciever through the headphone jack and i get a "hum" when my reciever is on. It's not god-awful, but I can still hear it and it bugs me. It is, however, especially bad with the subwoofer on. Huge hum comes out of it. And, of course, the hum gets louder as I turn up the volume. Check out my profile to see what I've got. I was just wondering if there was anything I could do to eliminate/minimize the "hum". Also, my comp and reciever are plugged into different outlets, if that makes a difference. Any help/suggestions would be greatly appreciated. Thanks.